there are other factors at play. As an example, much of Europe... particular the countries with the best intergenerational mobility... has MUCH lower income disparity. With lower income disparity, the difference in income between the quintiles becomes less significant and some of the normal intergenerational earnings movement you would see between income quintiles in Europe would still only be WITHIN a quintile in the US. Moving from the bottom quintile to the top quintile in Denmark is not THAT big a deal because the difference is not nearly as great. But moving from the bottom quintile to the top quintile in the US is a HUGE difference.